Journal of Tea Science Research, 2024, Vol.14, No.1, 57-63 http://hortherbpublisher.com/index.php/jtsr 60 Temperature is another critical factor, with 30 °C being the optimum for A. sydowii NRRL250 to degrade caffeine (Zhou et al., 2018a). This temperature facilitates the metabolic processes of the fungus, allowing for efficient degradation of caffeine into its metabolites. The pH of the medium also plays a crucial role in the degradation process. A pH of 6 was found to be optimal for A. sydowii NRRL250, which aligns with the slightly acidic conditions typically found in tea fermentation processes (Zhou et al., 2018a). This pH level supports the enzymatic activities necessary for the breakdown of caffeine molecules. In conclusion, the optimization of caffeine degradation conditions by Aspergillus sydowii involves careful control of substrate concentration, reaction temperature, and pH, which are all critical factors that influence the efficiency of the degradation process and the production of valuable metabolites such as theophylline and 3-methylxanthine (Zhou et al., 2018a; Zhou et al., 2018b). 4 Impact of Microbial Fermentation on Caffeine Content The impact of microbial fermentation on caffeine content in tea has been a subject of interest due to its implications for the flavor, health benefits, and commercial value of the final product. Recent studies have shed light on the complex interactions between microorganisms and caffeine during the fermentation process. A study focusing on the use of single microorganisms during fermentation revealed that molds, particularly Aspergillus niger van Tieghem, significantly increased the caffeine content in green tea leaves. The caffeine content was observed to rise from an initial 3.47% to 9.63% by the 16th day of fermentation, marking an increase rate of 177.5%. This suggests that certain molds may have a unique ability to enhance caffeine levels, potentially through a biosynthetic route that differs from the one in tea plants, with theophylline being a possible precursor to caffeine in this microbial context (Wang et al., 2008). In contrast, yeasts were found to decrease caffeine content during fermentation. This differential effect of molds and yeasts on caffeine levels indicates that the choice of microorganism in tea fermentation can be strategically used to control the caffeine content in the final product (Wang et al., 2008). Aspergillus sydowii, another fungus with a high caffeine-degrading capacity, was studied for its role in the solid-state fermentation (SSF) of Pu-erh tea. The presence of A. sydowii in sun-dried green tea leaves led to significant changes in the tea's chemical composition, including amino acids, carbohydrates, flavonoids, and caffeine metabolism. Notably, A. sydowii promoted the production of theophylline through the demethylation of caffeine, with about 93.24% of degraded caffeine being converted to theophylline (Zhou et al., 2020a). Furthermore, the microbial diversity in Xiaguan Tuo Tea during pile fermentation was investigated, revealing that fungi, particularly molds in the early stages and yeasts in the later stages, dominated the microbial population. This microbial activity resulted in a 59% increase in caffeine content by the end of the fermentation process (Li et al., 2018). The role of food microorganisms in caffeine degradation was also explored, with Lactobacillus casei, Leuconostoc mesenteroides, Rhizopus oryzae, and Saccharomyces cerevisiae demonstrating the ability to reduce caffeine content in robusta beans. These microorganisms transformed caffeine into dimethylxanthine and then into methylxanthine, following two distinct degradation patterns (Purwoko et al., 2023). In summary, microbial fermentation has a profound impact on the caffeine content of tea, with specific microorganisms either increasing or decreasing caffeine levels. Molds, particularly Aspergillus species, have been shown to increase caffeine content, while yeasts tend to decrease it. The choice of microorganism in the fermentation process can thus be a critical factor in determining the caffeine content and, consequently, the commercial and health-related properties of the tea (Wang et al., 2008; Li et al., 2018; Zhou et al., 2020a; Purwoko et al., 2023).
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